Interactive: What will 2C and 4C of warming mean for sea level rise?

OceansInteractive: What will 2C and 4C of warming mean for sea level rise?

Global warming of 4C above pre-industrial levels would raise sea levels by nearly nine metres, enough to submerge land currently home to more than half a billion people worldwide.

This comes from a new report by Climate Central, looking at what it would mean for different parts of the world if we continue to emit greenhouse gases at the speed we currently are.

This is a middle estimate for 4C – the amount of sea level rise that level of warming would lock us into could be high as 10.8 metres or as low as 6.9 metres, the report says.

It would be a steady climb, with sea levels taking centuries to rise this far. But our unrestrained emissions would mean we’re effectively locked in, making the rise unavoidable.

If emissions are kept in check, however, and we achieve the international goal of limiting warming to 2C, the risks don’t disappear, but they do come down a lot. The number of people worldwide living on land that would eventually become submerged could drop as low as 130m.

Today’s report is a global update to a paper published last month, which looked at sea level rise in the US. Ahead of the Paris climate talks, it’s meant as a demonstration of what’s at stake.

Have a go yourself. Below is an interactive map the scientists created. The left-hand side shows how the city of London would look with 4C of warming, while the right shows the same under 2C.

Click on the full version to select a location and see how sea level rise compares around the globe with 2C or 4C of warming..

I don’t understand why the estimated sea level rise is so low (9m for 4°C of global warming, or just over 2m per degree). Palaeoclimate data generally shows the rise to be an order of magnitude larger than this. For example, during the last deglaciation, sea level rose 120m for 5°C of global warming, which is over 20m per degree. We still have land ice amounting to 80m of sea level rise equivalent, mainly on Greenland and Antarctica. Is there a good physical reason to expect the rate to slow down by an order of magnitude, precisely at Holocene temperature and above?